Polyurethane foams are widely used in automotive, housing and other industries. The foams are produced through the reaction of a polyisocyanate with a polyol in the presence of various additives. One class of additives which is particularly effective as blowing agents is the chlorofluorocarbons (CFCs). CFCs vaporize as a result of the reaction exotherm during polymerization and cause the polymerizing mass to form a foam. However, the discovery that CFCs deplete ozone in the stratosphere has resulted in mandates for restricting CFC use. Therefore, more efforts have gone into the development of alternatives to CFCs for forming urethane foams and water blowing has emerged as an important alternative. In this method, blowing occurs from carbon dioxide generated by the reaction of water with the polyisocyanate. Foams can be formed by a one-shot method or by formation of a prepolymer and subsequent reaction of the prepolymer with water in the presence of a catalyst to form the foam. Regardless of the method, a balance is needed between reaction of the isocyanate and the polyol (gelling) and the reaction of the isocyanate with water (blowing) in order to produce a polyurethane foam in which the cells are relatively uniform and the foam has specific properties depending on the anticipated application; for example, rigid foams, semi-rigid foams, and flexible foams.
The ability of the catalyst to selectively promote either blowing or gelling is an important consideration in selecting a catalyst for the production of a polyurethane foam with specific properties. If a catalyst promotes the blowing reaction to too high a degree, carbon dioxide will be evolved before sufficient reaction of isocyanate with polyol has occurred. The carbon dioxide will bubble out of the formulation, resulting in collapse of the foam and production of a poor quality foam. At the opposite extreme, if a catalyst promotes the gelling reaction too strongly, a substantial portion of the carbon dioxide will be evolved after a significant degree of polymerization has occurred. Again, a poor quality foam is produced; characterized by high density, broken or poorly defined cells, or other undesirable features. Frequently, a gelling catalyst and a blowing catalyst are used together to achieve the desired balance of gelling and blowing in the foam.
Tertiary amine catalysts have been used in the production of polyurethanes. The tertiary amine catalysts accelerate both blowing (reaction of water with isocyanate to generate carbon dioxide) and gelling (reaction of polyol with isocyanate) and have been shown to be effective in balancing the blowing and gelling reactions to produce a desirable product. However, typical tertiary amines used as catalysts for polyurethane production generally have offensive odors and many are highly volatile due to low molecular weight. Release of tertiary amines during polyurethane production may present safety and toxicity problems, and release of residual amines from consumer products is generally undesirable.
Various alternatives to low molecular weight tertiary amine catalysts have been reported in the prior art. Examples are described below:
U.S. Pat. No. 3,073,787 (Krakler, 1963) discloses an improved process for preparing isocyanate foams in which a 3-dialkylaminopropionamide and 2-dialkylaminoacetamide are used as catalysts.
U.S. Pat. No. 4,007,140 (Ibbotson, 1977) discloses the use of various tertiary amines such as N,N'-bis(3-dimethylaminopropylamino)urea as low odor catalysts for the manufacture of polyurethanes.
U.S. Pat. No. 4,049,591 (McEntire et al., 1977) discloses a group of .beta.-substituted bis (N,N-dimethylaminopropyl) amines as polyurethane catalysts. The substitution group can be cyano, amide, ester, or ketone.
U.S. Pat. No. 4,094,827 (McEntire, 1978) discloses the use of certain alkyl substituted ureas, such as N,N-bis(dimethylaminopropyl)urea, as catalysts in the production of polyurethane foam.
U.S. Pat. No. 4,194,069 (Speranza et al., 1980) discloses the use of N-(3-dimethylaminopropyl)-N'-(3-morpholinopropyl)urea as a catalyst for producing polyurethanes.
U.S. Pat. No. 4,248,930 (Haas et al., 1981) discloses new tertiary amine compounds, such as bis(dimethylamino-n-propyl)amine, as catalysts for the production of polyurethane resins.
U.S. Pat. No. 4,644,017 (Haas et al., 1987) discloses the use of diffusion stable amino alkyl ureas having tertiary amino groups in the production of a polyisocyanate addition product.
DE 3027796 (1982) (Derwent abstract 82-13914E) discloses the use of dialkyl aminoalkyl urea catalysts for the production of polyurethane foam. It is reported that no smell is generated at polyurethane preparation temperatures.
EP 799,821 (1997) discloses amine/amide catalysts, such as 3-[3-dimethyl-aminoproppyl]amino-N,N-dimethylpropanamide and 3-[3-dimethylaminopropyl]amino-N-[3-dimethylaminopropyl]propanamide, for formation of polyurethanes. The catalysts are reported to have low fugitivity due to their reactivity with isocyanates.
U.S. Pat. No. 5,824,711 (Kimock et al., 1998) discloses N,N,N'-trimethylbis(aminoethyl)ether substituted urea compositions for the production of polyurethanes.
U.S. Pat. No. 5,874,483 (Savoca et al., 1999) discloses aminopropylbis(aminoethyl)ether compositions for the production of polyurethanes.